This invention relates generally to the process of the removal of mercury from waste streams in an industrial environment. More specifically, the present invention is directed to the removal of mercury from a solution of hydroxylammonium nitrate, such as hydroxy/ammonium/nitrate (HAN).
A common process to remove mercury from waste streams of chlor-alkali plants is the use of a sulfide treatment to produce a very insoluble mercury sulfide precipitate that can be filtered and removed from the liquid flow stream.
Mercury presence in solutions, such as those which derive from the decomposition of hydroxylammonium nitrate, present an additional problem which prevents the standard sulfide treatment from being effective. Normally, the decomposition of the HAN has occurred via a previous hypochlorite treatment step. The addition of sulfide or a sulfide treatment to HAN based nitrate a solution where decomposition of the HAN has not occurred does not effectively remove mercury.
These problems are solved by the process of the present invention which removes all of the hypochlorite prior to treating the solution to precipitate out the mercury as a sulfide and permit its removal by filtration.